Cooled vane cluster

ABSTRACT

A cast vane cluster with enhanced cooling contains an inner and an outer platform and at least two airfoils for directing a primary fluid stream axially rearward. A duct is bounded by inner, an outer endwall surfaces, and adjacent airfoil fluid directing surfaces. One or more cooling holes in the duct are drilled using an electrodischarge machine (EDM) method without a line of sight from the drilling equipment to the cooling hole location. One or more cooling holes, located in portions of the duct, may not be visible when viewed from an external location. Additionally, one or more cooling holes may only have an outlet cross sectional area visible when viewed along a longitudinal axis from an external location.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application discloses subject matter related to co-pending U.S.application “HOLE-DRILLING GUIDE AND METHOD” (APPLICANT REFERENCE NUMBEREH-10851). The disclosure of which is incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with Government support under N00019-02-C-3003awarded by the United States Navy. The Government has certain rights inthis invention.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The invention relates to gas turbine engine components, and moreparticularly to a cast vane cluster with enhanced cooling.

(2) Description of the Related Art

A gas turbine engine includes a compressor for directing a primary fluidstream axially rearward, through a combustor and into a turbine. Theturbine extracts power from a primary fluid stream and transmits thepower through a shaft to rotate the forward-mounted compressor. Aportion of the primary fluid stream is also directed to one or moresecondary fluid streams for use in cooling components of the gas turbineengine. Disposed within the turbine section are alternating, annularstages of rotating blades and stationary vanes. The blades and vanes aredisposed circumferentially about a central, longitudinal axis of the gasturbine engine.

Individual turbine vanes are comprised of an inner platform, an outerplatform and an airfoil spanning radially outward from the innerplatform to the outer platform. The airfoil contains a forward facingleading edge and a rearward facing trailing edge. The airfoil isstaggered on the platforms in relation to the primary fluid streamdirection, with the airfoil trailing edges of adjacent vanes forming anoverlapping array. Together, the platforms and airfoils of adjacentvanes bound a duct for directing the primary fluid stream rearward. Aninlet to the duct is bounded by adjacent airfoil leading edges and innerand outer endwall surfaces. An outlet to the duct is bounded by adjacentairfoil trailing edges and inner and outer endwall surfaces. The ductarea generally converges in the axially rearward direction.

Vanes are typically investment cast of high-strength Nickel or Cobaltalloys and may contain multiple airfoils within a single casting. Vanecastings with multiple airfoils are referred to as cast vane clustersand have the advantage of reducing the number of inter-platforminterfaces in a turbine stage. Inter-platform interfaces are costly tomanufacture and are a source of primary fluid stream leakage, which isdetrimental to the operating efficiency of the gas turbine engine.

In cast vane clusters requiring cooling, one or more hollow passagesextend through the interior of the airfoils forming a series of internalairfoil surfaces. The hollow passages direct a secondary fluid streaminto the interior of the cast vane cluster. A multitude of cooling holespass through the airfoil walls and into the hollow passages, allowingthe secondary fluid stream to discharge into the primary fluid stream.Each hole comprises an inlet, an outlet and a bore extending from theinlet to the outlet along a central, longitudinal axis. Preferably, themultitude of cooling holes are drilled from the direction of the airfoiltrailing edge and at an acute angle to the cast vane cluster surfaces.The drilling direction and angle are necessary to ensure that thesecondary fluid stream is discharged in a substantially rearwarddirection. This optimizes the cooling effectiveness of the secondaryfluid stream and reduces aerodynamic losses in the primary fluid stream.

Typically, cooling holes are drilled after a vane cluster casting ismade. The standard methods used for drilling cooling holes in castarticles are laser and electrodischarge machining (EDM). Laser drillingmethods utilize short pulses of a high-energy beam, an example is shownin U.S. Pat. No. 5,037,183. Electrodischarge machining (EDM) drillingmethods pass an electrical charge through a gap between an electrode anda surface, an example is shown in U.S. Pat. No. 6,403,910. Both thelaser and the EDM drilling methods require a line of sight from thedrilling equipment to the hole location, limiting the surfaces that maybe drilled.

Due to the stagger of the airfoils on the platforms of a cast vanecluster, portions of the duct surfaces are obstructed by the airfoiltrailing edges and cannot be drilled using conventional laser or EDMdrilling methods. The durability of cast vane clusters would be vastlyimproved if cooling holes could be placed wherever needed on the ductsurfaces. What is needed is a cast vane cluster with cooling holesdrilled into portions of the duct without a line of sight from thedrilling equipment to the hole location.

BRIEF SUMMARY OF THE INVENTION

Provided is a cast vane cluster with cooling holes drilled into surfaceswithout a line of sight from the drilling equipment to the holelocation.

In accordance with an exemplary embodiment, a cast vane cluster withenhanced cooling contains an inner and an outer platform and at leasttwo airfoils for directing a primary fluid stream axially rearward. Aduct is bounded by inner, an outer endwall surfaces, and adjacentairfoil fluid directing surfaces. The duct boundary contains at leastone cooling hole for directing a secondary fluid stream to enhancecooling and extend the life of the cast vane cluster.

Other features and advantages will be apparent from the following moredetailed descriptions, taken in conjunction with the accompanyingdrawings, which illustrate, by way of example, a preferred embodimentcast vane cluster with enhanced cooling.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a simplified schematic of a gas turbine engine along alongitudinal axis.

FIG. 2 is an isometric view of a cast vane cluster of the type used inthe gas turbine engine of FIG. 1.

FIG. 3 is a sectional top view of a cast vane cluster of FIG. 2 showingan obstructed surface area.

FIG. 4 is an isometric view of an embodiment of a hole drilling guidefor use in drilling holes into an obstructed surface area of a cast vanecluster.

FIG. 5 is an isometric view of an alternate embodiment of a holedrilling guide for use in drilling holes into an obstructed surface areaof a cast vane cluster.

FIG. 6 is a sectional top view of a cast vane cluster of FIG. 2 showinga hole-drilling guide of FIG. 4 in place.

FIG. 7 is a sectional side view of a cast vane cluster of FIG. 2 showinga hole-drilling guide of FIG. 4 in place.

FIG. 8 is a sectional side view of a vane cluster of FIG. 2 showing ahole-drilling guide of FIG. 5 in place.

FIG. 9 is a partial sectional view of a cooling hole of a cast vanecluster of FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

A gas turbine engine 10 with a central, longitudinal axis 12 is shown inFIG. 1. The gas turbine engine contains a compressor section 14, acombustor section 16 and a turbine section 18. A primary fluid stream 20is directed axially rearward from the compressor section 14, through thecombustor section 16 and into the turbine section 18. Within thecompressor section 14, a portion of the primary fluid stream 20 isdirected to one or more secondary fluid streams 22, which bypass thecombustor section 16, for use in cooling components within the gasturbine engine 10. The turbine section 18 typically comprises multiple,alternating stages of rotating blades 24 and stationary vanes 26.Multiple vanes may be cast as a single piece, which is typically calleda cast vane cluster 32 (shown in FIG. 2).

A cast vane cluster 32 comprises an inner platform 34, an outer platform36 and at least two airfoils 38 spanning radially outward from the innerplatform 34 to the outer platform 36. The inner platform 34 has an innerendwall surface 40 facing the airfoils and one or more inboard cavities42 (shown in FIGS. 7 and 8) opposite the airfoils. The outer platform 36has an outer endwall surface 44 facing the airfoils and one or moreoutboard cavities 46 opposite the airfoils. As shown in FIG. 3, each ofthe airfoils 38 are comprised of a concave fluid directing surface 48, aconvex fluid directing surface 50, a forward facing leading edge 52 anda rearward facing trailing edge 54. Collectively, the platform endwallsurfaces 40, 44 and airfoil fluid directing surfaces 48, 50 delineate aduct 56, as shown in FIG. 2, for directing the primary fluid stream 20rearward. One or more hollow passages 58 extend through the interior ofthe airfoils 38, connecting the inboard 42 and outboard cavities 46,(shown in FIG. 8). In surfaces that have a line of sight from a drillingequipment direction 60, a multitude of cooling holes 62 may be drilledusing conventional laser or electrodischarge machining EDM drillingmethods.

A typical cooling hole 62, as shown in FIG. 9, is comprised of an inletcross sectional area 65, an outlet cross sectional area 66 and a bore67. The bore 67 extends through an airfoil wall 94, from the inlet crosssectional area 65 to the outlet cross sectional area 66, along acentral, longitudinal axis 68. Although this example shows a coolinghole 62 with circular inlet and outlet cross sectional areas 65, 66, itis to be understood that any shape may be used. In addition, a coolinghole 62 may pass through an inner platform 34 or an outer platform 36 aswell as an airfoil wall 94.

Each of FIGS. 6,7 and 8, shows an exemplary embodiment cast vane clusterincluding one or more cooling holes 62 located in an obstructed area 64(shown in FIG. 3) of duct 56 (shown in FIG. 2). Duct 56, extends axiallyacross portions of the platform endwall surfaces 40, 44, and radiallyacross portions of the airfoil fluid directing surfaces 48, 50. One ormore cooling holes 62, located in portions of the duct 56, may not bevisible when viewed from an external location. Additionally, one or morecooling holes 62, may only have an outlet cross sectional area 66visible when viewed along a longitudinal axis 68 from an externallocation. An exemplary cast vane cluster, with enhanced cooling asdescribed above, may be made using one or more of the hole-drillingguides and methods described below.

FIG. 4 shows an embodiment of a hole-drilling guide 70 for guiding aflexible, hole-drilling instrument 72 to a surface without a line ofsight from the hole drilling equipment to a required hole location. Thehole-drilling guide 70 comprises a body 74, one or more inlet apertures76, one or more exit apertures 78 and a hollow, nonlinear raceway 80connecting each corresponding inlet 76 and exit 78 apertures. Shown inthis example are three raceways; however, any number may be used. Aninlet aperture 76 may contain a conical, bell-shaped or a similar shapedentrance 82 to simplify insertion of the flexible, hole-drillinginstrument 72. The raceways 80 are a similar cross sectional shape asthe flexible, hole-drilling instrument 72 and are slightly larger insectional area. The clearance required between the flexible,hole-drilling instrument 72 and the nonlinear raceway 80 depends on thematerial of the hole-drilling guide 70 and the degree of curvature ofthe nonlinear raceway 80. In this example, a radial clearance ofapproximately 0.004 inch is used. Each of the exit apertures 78penetrates a substantially conforming face 84 of the hole-drilling guide70. The position of an exit aperture 78 in relation to an obstructedsurface of an article is controlled by the substantially conformingfaces 84, and by other locating features such as rolls, pins, tabs,balls, bumps 86. A clamping lug 88 allows the hole-drilling guide 70 tobe rigidly secured to the article, once positioned.

FIG. 5 shows an alternate embodiment of a hole-drilling guide 70. In theembodiment shown, the hole-drilling guide 70 comprises a body 74 andfaces 84, which substantially conform to an internal cavity or passageof an article. A clamping lug 88 allows the hole-drilling guide 70 to berigidly secured to the article, once positioned, and contains one ormore inlet apertures 76. One or more exit apertures 78 penetrate thesubstantially corresponding surfaces 84 and are connected to the inletapertures 76 by one or more nonlinear raceways 80. Shown in this exampleare three nonlinear raceways; however, any number may be used.

In each of the above-described embodiments, the flexible, hole-drillinginstrument 72 is an EDM electrode. The EDM electrode is formed of aflexible, electrically conductive wire with a diameter of betweenapproximately (0.009-0.016) inches. For noncircular shaped holes, aflexible, electrically conductive foil strip of a comparable dimensionmay be used. The body 74 of the hole-drilling guide 70 is preferablymade of an electrically insulating material using solid freeformfabrication, casting, molding, machining or any other suitabletechnique. Alternately, the body 74 may be formed of an electricallyconductive material and the nonlinear raceways 80 may be coated with anelectrically insulating material.

In one aspect of a hole-drilling method, shown in FIG. 6, ahole-drilling guide 70 is used to guide an EDM electrode 72 to a portionof an obstructed surface area 64 (shown in FIG. 3) of a cast vanecluster 32. In this example, the obstructed surface area is located onan airfoil convex fluid directing surface 50. A cast vane cluster 32 isloaded in a single or multiple axis EDM station using a conventionaltooling fixture 90. In this example, an AMCHEM model HSD6-11, high-speedEDM station was used. A hole-drilling guide 70 is placed into a duct 56(shown in FIG. 2) of the cast vane cluster 32 and accurately positionedin relation to the cast vane cluster 32 by conforming surfaces 84 and alocating feature 86. The hole-drilling guide 70 is rigidly secured by aclamp 92 contacting a clamping lug 88. An EDM electrode 72 is insertedinto an inlet aperture 76 and advanced along a nonlinear raceway 80,until the electrode contacts the airfoil convex fluid directing surface50. Once loaded into the raceway 80, the EDM electrode 72 is secured tothe EDM station and plunged through an airfoil wall 94 into a hollowpassage 58, forming a hole 62. Upon completion of the hole 62, the EDMelectrode 72 is retracted and the process is repeated as required.

In another aspect of a hole-drilling method, shown in FIG. 7, ahole-drilling guide 70 is used to guide an EDM electrode 72 to a portionof an obstructed surface area 64 (shown in FIG. 3) of a cast vanecluster 32. In this example, the obstructed surface area is located onan inner endwall surface 40. A cast vane cluster 32 is loaded in asingle or multiple axis EDM station using a conventional tooling fixture90. In this example an AMCHEM model HSD6-11, high-speed EDM station orequivalent may be used. A hole-drilling guide 70 is placed into a duct56 (shown in FIG. 2) of the cast vane cluster 32 and accuratelypositioned in relation to the cast vane cluster 32 by a conformingsurface 84. The hole-drilling guide 70 is rigidly secured by a clamp 92contacting a clamping lug 88. An EDM electrode 72 is inserted into aninlet aperture 76 and advanced along a nonlinear raceway 80, until theelectrode contacts the inner endwall surface 40. Once loaded into theraceway 80, the EDM electrode 72 is secured to the EDM station andplunged through an inner platform 34 into an inner cavity 42 of the vanecluster 32, forming a hole 62. Upon completion of the hole 62, the EDMelectrode 72 is retracted and the process is repeated as required.

In yet another aspect of a hole-drilling method, shown in FIG. 8, ahole-drilling guide 70 guides an EDM electrode 72 to a portion of anobstructed surface area 64 (shown in FIG. 3) of a cast vane cluster 32.In this example, the obstructed surface area is located on an airfoilconcave fluid directing surface 48, and is accessed via a hollow passage58. A cast vane cluster 32 is loaded in a single or multiple axis EDMstation using a conventional tooling fixture 90. In this example, anAMCHEM model HSD6-11, high-speed EDM station or equivalent may be used.A hole-drilling guide 70 is inserted into the hollow passage 58 of thevane cluster 32 and accurately positioned in relation to the hollowpassage 58 by conforming surfaces 84 and locating features 86. Thehole-drilling guide 70 is rigidly secured by a clamp 92 contacting aclamping lug 88. An EDM electrode 72 is inserted into an inlet aperture76 and advanced along a nonlinear raceway 80, until the electrodecontacts the surface of the hollow passage 58. Once loaded into theraceway 80, the EDM electrode 72 is secured to the EDM station andplunged through the airfoil wall 94, forming a hole 62 (not shown. Uponcompletion of the hole 62, the EDM electrode 72 is retracted and theprocess is repeated as required.

The foregoing has described a cast vane cluster with enhanced coolingand its method of manufacture. It will be apparent to those skilled inthe art that various modifications thereto can be made without departingfrom the spirit and scope of the invention as described in the appendedclaims.

1. A vane cluster comprising: An inner platform including an innerendwall surface and an inboard cavity; An outer platform including anouter endwall surface and an outer cavity wherein said outer platform isspaced radially outboard of said inner platform and said outer endwallsurface faces said inner endwall surface; At least two airfoils spanningbetween said inner and outer endwall surfaces, each including a concavesurface, a convex surface, a leading edge and a trailing edge locatedaxially rearward of said leading edge, wherein said concave and convexsurfaces of adjacent airfoils face each other; A duct bounded by saidadjacent concave and convex surfaces and said inner and outer endwallsurfaces; At least one hole including an inlet cross sectional area andan outlet cross sectional area; and wherein said at least one holeoutlet cross sectional area is located on said duct boundary.
 2. A vanecluster comprising: An inner platform including an inner endwall surfaceand an inboard cavity; An outer platform including an outer endwallsurface and an outer cavity wherein said outer platform is spacedradially outboard of said inner platform and said outer endwall surfacefaces said inner endwall surface; At least two airfoils spanning betweensaid inner and outer endwall surfaces, each including a concave surface,a convex surface, a leading edge and a trailing edge located axiallyrearward of said leading edge, wherein said concave and convex surfacesof adjacent airfoils face each other; A duct bounded by said adjacentconcave and convex surfaces and said inner and outer endwall surfaces;At least one hole including an inlet cross sectional area and an outletcross sectional area; and wherein said at least one hole is not visiblewhen viewed from a location external of said duct region.
 3. The vanecluster of claim 2 wherein said external location is axially rearward ofsaid trailing edges.
 4. The vane cluster of claim 2 wherein saidexternal location is axially forward of said leading edges.
 5. A vanecluster comprising: An inner platform including an inner endwall surfaceand an inboard cavity; An outer platform including an outer endwallsurface and an outer cavity wherein said outer platform is spacedradially outboard of said inner platform and said outer endwall surfacefaces said inner endwall surface; At least two airfoils spanning betweensaid inner and outer endwall surfaces, each including a concave surface,a convex surface, a leading edge and a trailing edge located axiallyrearward of said leading edge, wherein said concave and convex surfacesof adjacent airfoils face each other; A duct bounded by said adjacentconcave and convex surfaces and said inner and outer endwall surfaces; Aduct inlet area bounded by said at least two airfoil leading edges, saidinner endwall surface and said outer endwall surface; A duct outlet areabounded by said at least two airfoil trailing edges, said inner endwallsurface and said outer endwall surface; At least one hole including aninlet cross sectional area, an outlet cross sectional area, a boreextending between said inlet and said outlet areas wherein said bore hasa central, longitudinal axis; and Wherein said at least one outlet crosssectional area is located on said duct boundary and said at least oneinlet cross sectional area is not visible when viewed along saidlongitudinal axis from an external location.
 6. The vane cluster ofclaim 5 wherein said external location is located forward of said ductinlet area.
 7. The vane cluster of claim 5 wherein said externallocation is located rearward of said duct outlet area.
 8. The vanecluster of claim 5 further comprising at least one hollow passage,extending through an airfoil, said at least one hollow passage,communicating with said inboard and outboard cavities and forming aninternal airfoil surface.
 9. The vane cluster of claim 8 wherein said atleast one hole inlet cross sectional area is located on said internalairfoil surface.
 10. The vane cluster of claim 9 wherein said at leastone hole is formed using an electrodischarge machine method.
 11. Thevane cluster of claim 10 wherein said at least one hole outlet crosssectional area is circular shaped.